In one type of magnetic data storage and retrieval system, such as a disc drive, a magnetic medium stack assembly includes a magnetic medium (or a plurality of magnetic media), such as a disc, mounted about a motor hub (also known as a “spindle hub”). In one type of system, the motor hub is rotatably coupled to a spindle motor, which rotates the motor hub, and consequently, the magnetic medium. A clamp typically fixes the magnetic medium to the motor hub, such as by applying a compressive force on the magnetic medium, which may abut portions of both the hub and the clamp. During operation of the magnetic storage system, an actuator moves one or more transducing heads (or another type of data transfer member) to selected positions adjacent to a top surface of the magnetic medium in order to read magnetically-encoded data stored on the magnetic medium (e.g., by sensing magnetic flux transitions) and/or write data to the magnetic medium (e.g., by inducing magnetic flux transitions in the magnetic medium). In a magnetic disc, data is written in concentric, radially-spaced data tracks. The transducing head is typically supported above the magnetic medium by an air bearing (i.e., a cushion of air) above the magnetic medium, which results when the magnetic medium generates currents of air as it rotates at high speeds. A distance between the transducing head and magnetic medium during operation may be referred to as a “fly height” of the transducer (or the slider, which carries the transducer on the actuator).
In general, it is desirable for the clamp to exert a substantially uniform clamping force on the magnetic medium. For example, an even clamping force helps maintain a substantially flat magnetic medium top surface in order to, for example, help maintain a constant slider fly height. In addition, it may be desirable to minimize circumferential acceleration. Circumferential acceleration is the out-of-plane acceleration of an imaginary dot on a substantially circular track caused by circumferential curvature (e.g., waviness or otherwise uneven) of the top surface of the magnetic medium. The circumferential acceleration value is typically unique to the specific disc at a certain spin speed.
Circumferential acceleration may affect the ability of the transducing head, which is carried by the slider, to read or write to the magnetic medium. If the top surface of the magnetic medium is uneven, the air bearing between the magnetic medium and the slider may be uneven, resulting in an uneven slider fly height. Thus, the landscape of the top surface of the magnetic medium affects the path of the slider and transducing head.
Physical distortion of the magnetic medium attributable to an uneven clamping force may also lead to the generation of operational errors during reading and recording of data no the magnetic medium. For example, the physical distortion may distort the size of one or more bits, which are areas of the magnetic medium in which data is written.
In addition, it may be desirable for the magnetic medium to be capable of withstanding relatively high levels of shock without shifting with respect to the motor hub. If the magnetic medium shifts, the transducer may inadvertently read or write to incorrect data tracks. As areal densities increase and the concentric data tracks on a magnetic disc become smaller, the tolerance for the transducer to align with a data track decreases, and it becomes more important to minimize shifting of the magnetic medium relative to the motor hub.
From a manufacturing perspective, it is also desirable for the mode of attachment to be capable of being integrated into an efficient manufacturing process (e.g., high speed and high volume manufacturing). Thus, it is important to maintain a substantially stable magnetic medium position with respect to a point of reference, such as the motor hub.